Suresh Kumar

Abstract

(Main goals of the PhD thesis)

Layered double hydroxides (LDH) are common secondary phases in clays and cementitious materials used worldwide in engineered barriers for hazardous and nuclear waste disposal. There is growing evidence that Mg-Al LDH and similar mixed metal-metal hydroxide solids (“green rusts” if Mg-Fe LDHs) play an important role in the retardation of both cations and anions. Studies on amorphous calcium silicate hydroxo-hydrate phase (CSH phases) as the dominant mineral component in concretes has already been performed [1 and others], but much less is known for the LDH class of phases as another important host mineral. The prediction of the partitioning of such ions between LDH and aqueous solutions is hampered by the scarce information on thermodynamic properties of the host phase [2]. This projects aims at providing by laboratory experiments an internally consistent set of thermodynamic constants of such solid-solution systems. The present work is limited to LDH composition with bivalent Zn and Cu substituted for the Mg, and carbonate as the only anion, which will be synthesized by common methods, and characterized by classical mineralogical techniques like XRD, XRF, and FTIR spectroscopy. Wet-chemistry techniques will be used to determine major and trace element partitioning between the solids and aqueous solutions using ICP-MS. Gibbs energy minimization geochemical modeling will be used to derive fundamental thermodynamic data from the thus gained experimental concentration data. The project is embedded in research cooperation with the Waste Management Laboratory of the Swiss Paul-Scherrer-Institute which will perform similar studies but on radionuclide ions.